The present invention relates a multistage type transmission apparatus for a vehicle, which has forward gears and reverse (backstep) gears.
There has been a motorcycle or a small-sized vehicle such as a saddle-seat type having three or four-wheeler (for example, an off-road buggy), which is provided with a multistage transmission gear train serving as a transmission apparatus and having a plurality of forward gears and a single reverse gear.
In general, the forward gears of such a transmission apparatus constitute a return-type or rotary-type transmission mechanism in which a foot-operated forward shift lever is swung by a prescribed number of times to thereby turn stepwisely (in stages) a gearshift cam included in the transmission apparatus so as to drive a plurality of gearshift forks in turn, thus carrying out a switching operation for the gears. A switching operation to the reverse gear is carried out, on the other hand, by shifting first the forward gears to a neutral position and then turning an exclusive reverse shift lever provided independently to a reverse position.
Maintenance of the neutral position of the forward gears is prerequisite for making a shifting operation to the reverse gear. Accordingly, there is provided a shift restriction mechanism for restricting the shifting operation to the reverse gear, when the forward gears are shifted to the forward position, thus not being kept in the neutral position.
The above-mentioned shift restriction mechanism may not only make the transmission apparatus complicated and large-sized, but also disable a shifting operation to the reverse gear. When the shifting operation to the reverse gear is conducted, the reverse gear rotates integrally with the drive shaft through connection of a dog clutch to transmit power to a driving wheel. Collision of gears of the dog clutch, however, disables operation (swing) of the reverse shift lever. A rider must therefore keep the reverse shift lever in the reverse position until the reverse gear turns slightly to provide a reliable connection condition of the dog clutch, leading to a nuisance and an unease operability.
An object of the present invention is to solve or eliminate such defects or disadvantages as those in the prior art mentioned above and to provide a transmission apparatus for a vehicle, capable of providing a simple and compact structure and ease operability and permitting to achieve a reliable transmission respectively between forward gears and reverse gear to thereby make power transmission loss as small as possible and improve controllability of a gearshift fork for the reverse gear.
The above and other objects of the present invention can be achieved by providing a transmission apparatus for a vehicle having an engine unit housed in an engine case in which a crankshaft extends in a vehicle width direction, a clutch mechanism is disposed on one side thereof, a counter shaft and a drive shaft are disposed in parallel to each other behind the crankshaft and a transmission apparatus is provided for the counter shaft and the drive shaft, the transmission apparatus comprising:
a multistage transmission gear train provided for the counter shaft and the drive shaft to be in parallel to the crankshaft, the multistage transmission gear train including forward gears and a reverse gear;
a forward gearshift cam for controlling a switching operation of the forward gears, the forward gearshift cam being provided, on an outer periphery thereof, with a flange portion integrally formed therewith, the flange portion being formed with an arcuate cutout on a peripheral portion thereof; and
a reverse gearshift cam for controlling a switching operation of the reverse gear, the reverse gearshift cam being located in a vicinity of the forward gearshift cam so as to be in parallel thereto, the reverse gearshift cam being formed with a tongue-shaped projection on an outer periphery thereof so as to be engageable with the cutout of the forward gearshift cam,
wherein positions of the cutout and the projection in a circumferential direction are determined so that the reverse gearshift cam is permitted to turn to a reverse position at a time only when the forward gearshift cam turns to a neutral position, and at a time when the reverse gearshift cam turns to a reverse position, at least a portion of the projection engages with the cutout to prevent the forward gearshift cam from turning to a position other than the neutral position.
Preferred embodiments or examples of the present invention of the above aspect will additionally include the following characteristic features.
The projection has one peripheral side which faces the forward gearshift cam when the reserve gearshift cam is kept in a position other than the reverse position so as to provide substantially a straight line, and when the reserve gearshift cam is kept in the position other than the reverse position, the projection has a shape, which is determined so as to satisfy either one of conditions of (i) the one peripheral side passing through between the forward gearshift cam and the reverse gearshift cam to coincide substantially with a tangential line between an outer peripheral surface of the flange portion of the forward gearshift cam and an outer peripheral surface of the reverse gearshift cam and (ii) the one peripheral side being placed on a side of the reverse gearshift cam relative to the tangential line.
The transmission apparatus further comprises a pressing device for imparting force for turning the reverse gearshift cam around an axial line thereof in a direction for carrying out a reverse switching operation of the reverse gear to the reverse gearshift cam.
The cutout has a length in an axial direction of the forward gearshift cam, the length being determined so as to be substantially identical to a total value of a slide amount of a gearshift fork driven by the reverse gearshift cam to be slidable and a thickness of the projection.
The transmission apparatus may further comprise an auxiliary transmission gearshift cam for an auxiliary transmission gear train, which is provided coaxially with the reverse gearshift cam. The auxiliary transmission gearshift cam is shifted relative to the forward gearshift cam in an axial direction thereof.
The reverse gear of the multistage transmission train is arranged in the vicinity of an inner wall of an engine case, and the forward gear is provided with the first speed gear arranged in the vicinity of the reverse gear. The clutch mechanism is provided on an opposite side of the reverse gear and the first speed gear of the forward gears relative to the inner wall of the engine case.
According to the structures and characteristic features of the present invention mentioned above, in the case where the forward gearshift cam is arranged to the forward position, the reverse gearshift cam is not turned to the reverse position, and on the contrary, the reverse gearshift cam is arranged to the reverse position, the forward gearshift cam is not turned to any position other than the neutral position. It is therefore possible to achieve a reliable restrictive transmission between the forward gears and the reverse gear with a simple and compact structure of the transmission apparatus, and hence, a good and reliable operability can also be ensured.
According to the preferred embodiments or examples, it is possible to minimize a required amount of turning motion of the reverse gearshift cam to the reverse position so as to provide a good operability, while preventing the projection of the reverse gearshift cam from interfering with the forward gearshift cam, when the forward gearshift cam is put in the forward position.
Furthermore, in the arrangement of the pressing device, the pressing device continues pressing the reverse gearshift cam in the direction for carrying out the reverse switching operation until connection of the dog clutch is surely completed, even when the collision of the gears of the dog clutch occurs during the shifting operation to the reverse gear. It becomes unnecessary for a rider to keep the reverse shift lever in the reverse position, thus improving operability.
According to the specific length in an axial direction of the forward gearshift cam, which is determined so as to be substantially identical to (or larger than) a total value of a range in which a gearshift fork driven by the reverse gearshift cam is slidable, and a thickness of the projection, the reverse gearshift cam becomes not only turnable, but also slidable in the axial direction, improving controllability of the gearshift fork for the reverse gear.
Still furthermore, the arrangement of the common gearshift cam shaft permits to support, to be rotatable, the reverse gearshift cam and the auxiliary transmission gearshift cam to reduce the number of components and effectively use a space in the engine case, thus achieving a simple and compact structure of the transmission apparatus.
In the arrangement, in which the auxiliary transmission gearshift cam is shifted relative to said forward gearshift cam in an axial direction thereof, it is possible to prevent interference between the forward gearshift cam and the auxiliary transmission gearshift cam with the result that it is unnecessary to provide any restriction device for prevention of interference, thus further contributing to simplification of the transmission apparatus.
Still furthermore, in an arrangement, in which the reverse gear of the multistage transmission is placed in the vicinity of an inner wall of the engine case, and the first speed gear of the forward gears is placed in the vicinity of the reverse gear, it is possible to relieve a large transmission torque, which is applied to the reverse gear and the first speed gear of the forward gears, into the inner wall of the engine case. Flexure and torsion of the counter shaft and the drive shaft can therefore be prevented, thus making power transmission loss as small as possible.
According to the location of the clutch mechanism at the position mentioned above, it is possible to minimize the distance between the clutch mechanism, and the reverse gear and the first speed gear of the forward gears, so as to prevent occurrence of flexure and torsion of the counter shaft to which the clutch mechanism is connected, thus more effectively avoiding the power transmission loss.
It is further to be noted that the nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.